1. Field of the Invention
This invention relates to a vibratory motor which utilizes a traveling wave as a driving source.
2. Description of the Related Art
A conventional vibratory motor generates a traveling wave on a stator member and transmits energy of the vibration to a rotor member by a friction force between the stator and the rotor. Therefore, the rotor member should have a stable contact with the stator member so as to obtain a stable output.
FIGS. 2 and 3 show the conventional vibratory motor. Therein, a cone spring 53 is provided so as to press a rotor 52 to stator 51. The cone spring 53 maintains a stable contact between the stator 51 and the rotor 52.
During rotation of the rotor 52, it receives a vibratory impulse from the stator 51. As a result, the rotor 52 is vibrated in the normal direction and in the tangential direction (as shown in FIG. 3). At this time, the vibration which is generated on the rotor 52 is of the same frequency as the vibration of the stator 51. As long as the vibration of the rotor 52 is of the same frequency as the vibration of the stator 51, the output of the motor is increased in response to an increase of electric power supplied to the stator 51.
However, as soon as the supplied electric power exceeds an upper limit, the output of the motor is not increased. In this situation, a principal vibration may be generated on the rotor 52. The principal vibration weakens the vibration which has the same frequency with the stator 51.